Voyager 1: reports of my exit are greatly exaggerated

It launched 35 years ago today, but the most distant spacecraft from Earth is stubbornly refusing to leave home turf. NASA’s Voyager 1 has seemed on the verge of exiting our solar system for years, but new results suggest that it still has a way to go before it enters interstellar space.

The latest readings from one of the spacecraft’s instruments show that charged particles around Voyager 1 aren’t changing direction the way they should at the heliopause, the boundary between the sun’s sphere of influence and the rest of the galaxy.

This could be a sign that the craft won’t leave the solar system for up to 15 years, by which time it is expected to have run out of the power needed to communicate with Earth.

The solar system sits in a huge magnetic bubble. Solar wind containing charged particles flows outwards from the sun, only to get bent around by the magnetic field, at the heliopause.

But those measurements could not show whether the particles were in the process of changing direction to follow the curve of the heliopause. Getting the full picture meant turning the ageing spacecraft into an acrobat.

Beginning in 2011, mission managers commanded Voyager 1 to carry out a set of rolls, in which it rotated 70 degrees and held that orientation before returning to its previous orientation. The craft carried out a set of rolls, each lasting a few hours, once every other month for five months.

“Rolling the craft like that was an amazing thing to do,” says Voyager scientist Robert Decker. “It’s a tricky manoeuvre for such an old spacecraft.”

To the team’s surprise, the data showed little to no change in the wind’s direction.

Decker reckons the craft is in a transition zone not accounted for in current models of the heliosheath. He is not sure how big this region is, but based on Voyager 1’s readings of fluctuations in charged particles called cosmic rays, Decker stands by the popular idea that Voyager 1 could cross the heliopause by 2014 – perhaps even sooner.

Gary Zank of the University of Alabama in Huntsville, however, points out that the new, highly detailed measurements reveal very tiny flow changes. These were predicted by models of the solar wind which date back to 1997 and that specify a thicker outer shell for the solar bubble. This could keep Voyager 1 inside the solar system for another 10 to 15 years, he says.

If Zank is right, we may never get word of the crossing – optimistic estimates say the spacecraft’s power supply is due to run out in 2025.